The present invention relates to a technique effective when applied to a drive control technique for a brushless motor and startup control of a three-phase DC motor, and to a technique effective when applied to a drive control device of a spindle motor for rotationally driving a storage medium in a disk storage device such as a hard disk drive (HDD).
A brushless three-phase DC motor generally called a spindle motor is used to rotate a magnetic disk as a storage medium in a hard disk drive. The magnetic disk is rotated at high speed by the spindle motor, and a magnetic read/write head is brought close to the surface of the rotating magnetic disk and moved in a radial direction to write or read information. The following method has been conventionally used in drive control of a brushless motor: the positional relationship between a rotor and a stator is detected using a Hall element; a coil phase at which energization is to be started is determined from the detected positional relationship to prevent the reverse rotation of the motor.
However, providing the motor with a rotor position detector using a Hall element makes it difficult to downsize the device; therefore, a sensorless motor has come into greater use in the hard disk drive. In such a sensorless motor, uncertainty about the positional relationship between the rotor and the stator at the time of starting rotation may cause reverse rotation of the rotor. To cope with this, the present applicant has previously proposed the following control method: a pulse current of such a short duration that the rotor does not react is passed through any two phase coils; the polarity of an induced voltage that appears in a non-conducting phase is detected to determine the positional relationship between the rotor and the stator; the characteristic that the polarity of an induced voltage switches every 180 electrical degrees is utilized to determine a phase at which energization should be started; whereby reverse rotation of this sensorless motor at its start-up is avoided (see Japanese Unexamined Patent Publication No. 2001-275387, Japanese Unexamined Patent Publication No. 2004-140975, and Japanese Unexamined Patent Publication No. 2006-115599).